1. Field of the Invention
The present invention relates to a check valve having a back-flow preventing function and, more particularly, to a check valve used for the transport of an automotive fuel such as a gasoline, particularly a gasohol (alcohol-blended gasoline).
2. Description of the Art
For prevention of back-flow of a fluid, fluid lines such as automotive fluid lines are generally provided with a check valve, which is fixed to a midportion thereof (or at an end thereof) by means of a clamp. A cut-off valve and a duckbill valve, for example, are known as check valves having a back-flow preventing function.
A check valve is typically composed of a rubber material. A particularly preferred material for the check valve in terms of gasoline resistance, low-temperature resistance and pressure loss balance is a fluorosilicone rubber.
In recent years, public attention has been directed to environmental issues. In the United States, the use of methyl t-butyl ether (MTBE), which has conventionally been blended as an octane value increasing agent in gasoline, has been banned to help prevent ground water pollution. For use as an alternative to gasoline containing methyl t-butyl ether, gasohol containing an alcohol additive is now under consideration.
Even if such a gasohol is transported through a fluid line, the fluorosilicone rubber is still employed as the material for the check valve, because no limitation is imposed on the rubber material for the check valve.
However, where a check valve composed of ordinary fluorosilicone rubber for transport of gasohol is fixed to an automotive fuel line by means of the clamp, the check valve is liable to be damaged or cut by the clamp because the fluorosilicone rubber has a high swelling degree with respect to gasohol.
In view of the foregoing, it is an object of the present invention to provide a check valve which is free from clamp damage and has a satisfactory pressure loss balance even if being used with the gasohol.
In accordance with the present invention to achieve the aforesaid object, there is provided a check valve comprising a fluorosilicone rubber having:
(A) a tear strength of not smaller than 150 N/cm;
(B) an initial 100% tensile stress of not greater than 3.5 MPa;
(C) a 100% tensile stress of 1.8 to 3.0 MPa after immersion in a gasohol; and
(D) a volume swell of not greater than 35% after immersion in the gasohol.
The inventors of the present invention have conducted intensive studies to provide a check valve which is free from clamp damage even if being used with an automotive gasohol fuel. The inventors have found that, where a fluorosilicone rubber employed as a material for the check valve has a tear strength within a predetermined range, an initial 100% tensile stress within a predetermined range, a 100% tensile stress within a predetermined range after immersion in a gasohol and a volume swell within a predetermined range after immersion in the gasohol, the check valve has an excellent resistance to swelling by gasohol. As a result, the check valve tends to be free from clamp damage, so that the check valve can advantageously be used in an automotive fuel transport line in which the gasohol flows. Thus, the present invention has been attained.